BEST OF BREEDERS: Prolific pop Todd Whitehurst a few years ago with daughter-by-marriage Kathryn (lower right) and his sperm-donor offspring (left to right) Tyler, Virginia and Gavin.

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When he was a cash-strapped college student 20 years ago, Todd Whitehurst didn’t think too deeply on the consequences of donating sperm.

Then, when he was 41, he got an e-mail from a girl named Virginia. “She said, basically, ‘I’m 14, and I think I’m your daughter,’ ” explained Whitehurst, now a 45-year-old medical engineer.

Shortly after, he found a son, Tyler, now 14. And another, Gavin, now 16. That led to another child, and another, and yet another.

“It was definitely overwhelming,” Whitehurst said. “I’m not even sure how many children there are.”

So far he has found nine kids sired by his sperm. Statistically speaking, said one biogeneticist, Whitehurst could be the father of 42 to 60 children.

Thanks to a lack of industry regulation, high totals are all too probable, especially for prolific college kids like Whitehurst — who donated weekly for about three years, for $50 a pop, at a clinic on the Stanford University campus in the 1980s and ’90s. A Web site set up for the children of sperm donors has discovered a number of “superdads” who have fathered dozens, sometimes hundreds, of children.

One top seed in Virginia has sired an astounding 129 kids and counting, according to the Donor Sibling Registry, a nonprofit that helps connect families with biological fathers and siblings. Another donor, in the Boston area, has been traced to 72 kids, said Wendy Kramer, a mother to a sperm-donor child who started the online registry when her son began asking questions about his pop.

The registry has found 92 groups of 10 or more offspring, and 336 groups that have up to nine siblings, said Kramer.

There’s no limit on how many banks a donor can sell his sperm to — about 21 percent of donor dads have given to more than one, according to Kramer.

In theory, said Albert Anouna, director of Biogenetics and Sperm Bank of New York, cryo clinics should destroy a donor’s sperm after it has produced about 10 live births. Birth numbers are self-reported by pregnant moms — an incomplete and inconsistent system, Anouna acknowledged.

Compounding the problem, donors are screened so that the most fertile get selected, because high sperm count and good motility are most likely to produce a pregnancy, said Anouna. High-performers who rack up many pregnancies are among the most popular donors selected by women.

“Up until 1999, physicians could order a pool of vials for their patients. They’d come in and the doctor would say, ‘This one works fine — it’s already gotten three women pregnant. Why don’t you try it?’ ” said Anouna.

Whitehurst is one of a handful of donor dads to step forward and connect with his kids.

“It was pretty wild,” he said of receiving his initial e-mail from Virginia. “She had my donor number, which I hadn’t ever given anybody, and she sent a picture. She looked a lot like me.”

He e-mailed her back, and Virginia encouraged him to go to the Donor Sibling Registry. His donor number immediately turned up two other families, and later, three more. One of his donor moms actually has three kids from his semen.

A few years ago, Whitehurst, who has two kids from a prior marriage, traveled to meet Virginia, Tyler and Gavin.

Now Tyler and Gavin frequently share e-mails and phone calls with him, and Virginia, about to set off to his alma mater in the fall, seeks dating advice.

Whitehurst can’t help but regard his progeny like a typical proud papa — especially on this day, when the cards and phone calls roll in.

“I love Father’s Day,” he said. “I don’t usually think about the other children that may be out there on this day, as I like to focus on the children who I already know. It’s been a wonderful and enriching experience, and I am very happy that I have met them.”

Who’s your daddy?

* Excerpts from the Donor Sibling Registry, where children hope to connect with biological fathers and half-siblings.

* “Just wanted to tell those who are undecided whether or not to pursue half-sibling postings/contact … it is such an AMAZING journey!! My son now has 17 half-siblings! Not only are all our kids amazing, but the families are as well!!! It appears that the kids have similar characteristics in soooooo many ways! They look alike, have similar mannerisms and likes/dislikes! While there are differences, the similarities are just overwhelming!”

* “When I joined DSR, I was shocked to see how many 1⁄2 siblings my son has, and is still counting. There are about 30 we know of so far, awaiting word of another family member who just did an embryo transfer. What a shock and an amazement at the same time.”

* “Yes, there are 14 boys and three girls from Donor 3478. Not all posted on the DSR but made contact anyway. Besides three new siblings that we just found out about, we have become one big great extended family.”

* “I was bored one day and on a whim decided to join the registry. I had remembered a physical description that my mom had given me of my donor when I was 12. She had also mentioned that he was from the Fairfax VA cryobank. I used the browse by clinic feature and found a description that kind of fit what I had remembered. Not so long story short I met the guy after an email I sent and got a dna test. Turns out he was a match. The guy turned out to be Richard Hatch from that Survivor show on CBS.”